U.S. patent number 6,522,855 [Application Number 09/565,539] was granted by the patent office on 2003-02-18 for image forming apparatus and developing apparatus preventing uneven image density.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Tsuyoshi Imamura, Shunji Katoh, Shinichi Kawahara, Kazuhisa Sudo, Shinji Tamaki, Junichi Terai, Kiyonori Tsuda, Masayuki Yamane, Hideo Yoshizawa.
United States Patent |
6,522,855 |
Katoh , et al. |
February 18, 2003 |
Image forming apparatus and developing apparatus preventing uneven
image density
Abstract
A developing apparatus for use in an image forming apparatus
includes a developer bearing member having a magnetic field
generating device internally and configured to bear and convey
two-component developer including toner and magnetic carrier, a
first regulating member configured to regulate an amount of the
developer born and conveyed by the developer bearing member, a
developer container section for storing the developer scraped off
by the first regulating member, a second regulating member arranged
upstream of the first regulating member in a conveying direction of
the developer on the developer bearing member, and a toner
container section for supplying toner to the developer bearing
member. The developing apparatus changes a toner take-in condition
of the developer on the developer bearing member by changing a
contact condition between the developer and the toner according to
a change of a toner density of the developer on the developer
bearing member. A surface of the second regulating member facing
the developer bearing member has an area large enough to unify a
layer thickness of the developer on the image bearing member in the
axial direction of the developer bearing member.
Inventors: |
Katoh; Shunji (Sagamihara,
JP), Yoshizawa; Hideo (Urawa, JP), Tamaki;
Shinji (Tokyo, JP), Terai; Junichi (Yokohama,
JP), Tsuda; Kiyonori (Yokohama, JP),
Imamura; Tsuyoshi (Sagamihara, JP), Yamane;
Masayuki (Yokohama, JP), Sudo; Kazuhisa
(Kawasaki, JP), Kawahara; Shinichi (Tokyo,
JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
|
Family
ID: |
27471130 |
Appl.
No.: |
09/565,539 |
Filed: |
May 5, 2000 |
Foreign Application Priority Data
|
|
|
|
|
May 6, 1999 [JP] |
|
|
11-125601 |
May 6, 1999 [JP] |
|
|
11-126007 |
Jul 16, 1999 [JP] |
|
|
11-203408 |
Mar 15, 2000 [JP] |
|
|
2000-072309 |
|
Current U.S.
Class: |
399/274;
399/284 |
Current CPC
Class: |
G03G
15/09 (20130101) |
Current International
Class: |
G03G
15/09 (20060101); G03G 015/08 () |
Field of
Search: |
;399/274,284 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
63004282 |
|
Jan 1988 |
|
JP |
|
08202157 |
|
Aug 1996 |
|
JP |
|
08314277 |
|
Nov 1996 |
|
JP |
|
09197833 |
|
Jul 1997 |
|
JP |
|
10039638 |
|
Feb 1998 |
|
JP |
|
10149015 |
|
Jun 1998 |
|
JP |
|
Primary Examiner: Grainger; Quana M.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States:
1. A developing apparatus, comprising: a developer bearing member
having a magnetic field generating device internally and configured
to bear and convey two-component developer including toner and
magnetic carrier; a first regulating member configured to regulate
an amount of the developer born and conveyed by the developer
bearing member; a developer container section storing developer
scraped off by the first regulating member; a second regulating
member arranged upstream of the first regulating member in a
conveying direction of the developer on the developer bearing
member; and a toner container section for supplying toner to the
developer bearing member, wherein the developing apparatus changes
a toner take-in condition of the developer on the developer bearing
member by changing a contact condition between the developer and
the toner according to a change of a toner density of the developer
on the developer bearing member, a surface of the second regulating
member facing the developer bearing member has an area sized to
unify a layer thickness of the developer on the image bearing
member in an axial direction of the developer bearing member, the
second regulating member having a base portion with a first width
and an end portion with a second width, the second width being
larger than the first width, the surface of the second regulating
member facing the developer bearing member being provided on the
end portion, and the surface of the second regulating member facing
the developer bearing member is spaced from a surface of the
developer bearing member such that a gap between an end portion of
the facing surface of the second regulating member upstream in the
developer conveying direction and the surface of the developer
bearing member is larger than a gap between a downstream end
portion of the facing surface of the second regulating member and
the surface of the developer bearing member.
2. A developing apparatus according to claim 1, wherein, the
developer container section is formed downstream of the second
regulating member in the developer conveying direction, and the
facing surface of the second regulating member is extended toward
an upstream in the conveying direction of the developer on the
developer bearing member.
3. A developing apparatus according to claim 1, wherein the surface
of the second regulating member facing the developer bearing member
is elongated upstream in the developer conveying direction.
4. A developing apparatus according to claim 1, wherein the surface
of the second regulating member facing the developer bearing member
is planar.
5. A developing apparatus according to claim 1, wherein a deviation
of a magnetic force on the developer bearing member is set such
that the layer thickness of the developer passing through the
second regulating member is even.
6. A developing apparatus comprising: a developer bearing member
having a magnetic field generating device internally and configured
to bear and convey two-component developer including toner and
magnetic carrier; a first regulating member configured to regulate
an amount of the developer born and conveyed by the developer
bearing member; a developer container section for containing
developer scraped off by the first regulating member; a second
regulating member arranged upstream of the first regulating member
in a conveying direction of the developer on the developer bearing
member; and a toner container section for supplying toner to the
developer bearing member, wherein the developing apparatus changes
a toner take-in condition of the developer on the developer bearing
member by changing a contact condition between the developer and
the toner according to a change of a toner density of the developer
on the developer bearing member, the second regulating member is
spaced from the developer bearing member so as to regulate an
increase of a layer thickness of the developer on the developer
bearing member when the layer thickness thereof is increased due to
a rise of the toner density of the developer, and a surface of the
second regulating member facing the developer bearing member is
spaced from a surface of the developer bearing member such that a
gap between an end portion of the facing surface of the second
regulating member upstream in the developer conveying direction and
the surface of the developer bearing member is larger than a gap
between a downstream end portion of the facing surface of the
second regulating member and the surface of the developer bearing
member, the second regulating member having a base portion with a
first width and an end portion with a second width, the second
width being larger than the first width, the surface of the second
regulating member facing the developer bearing member being
provided on the end portion.
7. A developing apparatus according to claim 6, wherein a first
normal component of a magnetic force, which is applied to developer
by the developer bearing member at a downstream end portion of the
surface of the second regulating member facing the developer
bearing member in the developer conveying direction, is set to be
larger than a second normal component of the magnetic force applied
to the developer by the developer bearing member at an upstream
portion of the surface of the second regulating member in the
developer conveying direction.
8. A developing apparatus according to claim 6, wherein a gap
between an end-most portion of the surface of the second regulating
member upstream in the developer conveying direction and the
developer bearing member is set to be larger than a layer thickness
of the developer on the developer bearing member.
9. A developing apparatus according to claim 6, wherein the surface
of the second regulating member facing the developer bearing member
is elongated upstream in the developer conveying direction.
10. A developing apparatus according to claim 6, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
11. A developing apparatus comprising: a developer bearing member
having a magnetic field generating device internally and configured
to bear and convey two-component developer including toner and
magnetic carrier; a first regulating member configured to regulate
an amount of the developer born and conveyed by the developer
bearing member; a developer container section for containing
developer scraped off by the first regulating member; and a toner
container section for supplying toner to the developer bearing
member, wherein the developer container section has a second
regulating member arranged upstream of the first regulating member
in a conveying direction of the developer on the developer bearing
member, the second regulating member is spaced from the developer
bearing member so as to regulate an increase of a layer thickness
of the developer on the developer bearing member when the layer
thickness of the developer is increased due to a rise of a toner
density of the developer, a surface of the second regulating member
facing the developer bearing member is spaced from a surface of the
developer bearing member such that a gap between an end portion of
the facing surface of the second regulating member upstream in the
developer conveying direction and the surface of the developer
bearing member is larger than a gap between a downstream end
portion of the facing surface of the second regulating member and
the surface of the developer bearing member, the second regulating
member having a base portion with a first width and an end portion
with a second width, the second width being larger than the first
width, the surface of the second regulating member facing the
developer bearing member being provided on the end portion, a
developer circulating portion is formed for circulating the
developer obstructed by the second regulating member, and a
developer stagnated portion, where the developer stands still when
the toner density of the developer is within a predetermined
appropriate range, is formed in a toner supplying path connecting
the toner container section with the developer circulating portion,
such that a condition of taking the toner into the developer is
changed by a change of a contact condition between the developer
and the toner according to a change of the toner density of the
developer on the developer bearing member, and the second
regulating member is configured so as to suppress a diffusion of
the developer circulating portion.
12. A developing apparatus according to claim 11, wherein, the
second regulating member includes a developer layer thickness
regulating section, which is spaced from the developer bearing
member so as to regulate an increase of a layer thickness of the
developer on the developer bearing member when the layer thickness
of the developer is increased due to a rise of a toner density of
the developer, and a circulating direction regulating section for
regulating a motion of the developer so that the developer
circulating portion does not diffuse toward the toner container
section when the developer obstructed by the developer layer
thickness regulating section moves toward an upstream in the
developer conveying direction to form the developer circulating
portion.
13. A developing apparatus according to claim 12, wherein the
circulating direction regulating section of the second regulating
member is a surface facing the developer bearing member extending
from the developer layer thickness regulating section toward the
upstream in the developer conveying direction.
14. A developing apparatus according to claim 11, wherein the
surface facing the developer bearing member of the second
regulating member is non-magnetic.
15. A developing apparatus according to claim 11, wherein the
surface of the second regulating member facing the developer
bearing member is elongated upstream in the developer conveying
direction.
16. A developing apparatus according to claim 11, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
17. A developing apparatus, comprising: a developer bearing member
having a magnetic field generating device internally and configured
to bear and convey two-component developer including toner and
magnetic carrier; a first regulating member configured to regulate
an amount of the developer born and conveyed by the developer
bearing member; a developer container section for containing
developer scraped off by the first regulating member; and a toner
container section provided adjacent to the developer container
section for supplying toner to the developer bearing member,
wherein the developer container section has a second regulating
member arranged upstream of the first regulating member in the
conveying direction of the developer on the developer bearing
member, the second regulating member is spaced from the developer
bearing member so as to regulate an increase of a layer thickness
of the developer on the developer bearing member when the layer
thickness of the developer is increased due to a rise of a toner
density of the developer, a surface of the second regulating member
facing the developer bearing member is spaced from a surface of the
developer bearing member such that a gap between an end portion of
the facing surface of the second regulating member upstream in the
developer conveying direction and the surface of the developer
bearing member is larger than a gap between a downstream end
portion of the facing surface of the second regulating member and
the surface of the developer bearing member, the second regulating
member having a base portion with a first width and an end portion
with a second width, the second width being larger than the first
width, the surface of the second regulating member facing the
developer bearing member being provided on the end portion, a
developer circulating portion is formed for circulating the
developer obstructed by the second regulating member, and a
developer stagnated portion, where the developer stands still when
the toner density of the developer is within a predetermined range,
is formed in a toner supplying path connecting the toner container
section with the developer circulating portion, such that a
condition of taking the toner into the developer is changed by a
change of a contact condition between the developer and the toner
according to a change of the toner density of the developer on the
developer bearing member, and a developing apparatus frame is
configured so as not to disturb an ear crack portion of the
developer which is formed on the developer bearing member by a
magnetic pole opposite to the developer circulating portion.
18. A developing apparatus according to claim 17, wherein the
surface of the second regulating member facing the developer
bearing member is elongated upstream in the developer conveying
direction.
19. A developing apparatus according to claim 17, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
20. An image forming apparatus, comprising: an image bearing member
for bearing a latent image; and a developing apparatus for
developing the latent image, the developing apparatus including; a
developer bearing member having a magnetic field generating device
internally and configured to bear and convey two-component
developer including toner and magnetic carrier; a first regulating
member configured to regulate an amount of the developer born and
conveyed by the developer bearing member; a developer container
section storing developer scraped off by the first regulating
member; a second regulating member arranged upstream of the first
regulating member in a conveying direction of the developer on the
developer bearing member; and a toner container section for
supplying toner to the developer bearing member, wherein the
developing apparatus changes a toner take-in condition of the
developer on the developer bearing member by changing a contact
condition between the developer and the toner according to a change
of a toner density of the developer on the developer bearing
member, a surface of the second regulating member facing the
developer bearing member has an area sized to unify a layer
thickness of the developer on the image bearing member in an axial
direction of the developer bearing member, the second regulating
member having a base portion with a first width and an end portion
with a second width, the second width being larger than the first
width, the surface of the second regulating member facing the
developer bearing member being provided on the end portion, and the
surface of the second regulating member facing the developer
bearing member is spaced from a surface of the developer bearing
member such that a gap between an end portion of the facing surface
of the second regulating member upstream in the developer conveying
direction and the surface of the developer bearing member is larger
than a gap between a downstream end portion of the facing surface
of the second regulating member and the surface of the developer
bearing member.
21. An image forming apparatus according to claim 20, wherein, the
developer container section is formed downstream of the second
regulating member in the developer conveying direction, and the
facing surface of the second regulating member is extended toward
an upstream in the conveying direction of the developer on the
developer bearing member.
22. An image forming apparatus according to claim 20, wherein a
deviation of a magnetic force on the developer bearing member is
set such that the layer thickness of the developer passing through
the second regulating member is even.
23. An image forming apparatus according to claim 20, wherein the
surface of the second regulating member facing the developer
bearing member is elongated upstream in the developer conveying
direction.
24. An image forming apparatus according to claim 20, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
25. An image forming apparatus, comprising: an image bearing member
for bearing a latent image; and a developing apparatus for
developing the latent image, the developing apparatus including: a
developer bearing member having a magnetic field generating device
internally and configured to bear and convey two-component
developer including toner and magnetic carrier; a first regulating
member configured to regulate an amount of the developer born and
conveyed by the developer bearing member; a developer container
section for containing developer scraped off by the first
regulating member; a second regulating member arranged upstream of
the first regulating member in a conveying direction of the
developer on the developer bearing member; and a toner container
section for supplying toner to the developer bearing member,
wherein the developing apparatus changes a toner take-in condition
of the developer on the developer bearing member by changing a
contact condition between the developer and the toner according to
a change of a toner density of the developer on the developer
bearing member, the second regulating member is spaced from the
developer bearing member so as to regulate an increase of a layer
thickness of the developer on the developer bearing member when the
layer thickness thereof is increased due to a rise of the toner
density of the developer, and a surface of the second regulating
member facing the developer bearing member is spaced from a surface
of the developer bearing member such that a gap between an end
portion of the facing surface of the second regulating member
upstream in the developer conveying direction and the surface of
the developer bearing member is larger than a gap between a
downstream end portion of the facing surface of the second
regulating member and the surface of the developer bearing member,
the second regulating member having a base portion with a first
width and an end portion with a second width, the second width
being larger than the first width, the surface of the second
regulating member facing the developer bearing member being
provided on the end portion.
26. An image forming apparatus according to claim 25, wherein a
first normal component of a magnetic force, which is applied to the
developer by the developer bearing member at a downstream end
portion of the surface of the second regulating member facing the
developer bearing member in the developer conveying direction, is
set to be larger than a second normal component of the magnetic
force applied to the developer by the developer bearing member at
an upstream portion of the surface of the second regulating member
in the developer conveying direction.
27. An image forming apparatus according to claim 25, wherein a gap
between an end-most portion of the surface of the second regulating
member upstream in the developer conveying direction and the
developer bearing member is set to be larger than the layer
thickness of the developer on the developer bearing member.
28. An image forming apparatus according to claim 25, wherein the
surface of the second regulating member facing the developer
bearing member is elongated upstream in the developer conveying
direction.
29. An image forming apparatus according to claim 25, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
30. An image forming apparatus, comprising: an image bearing member
for bearing a latent image; a developing apparatus for developing
the latent image, the developing apparatus including; a developer
bearing member having a magnetic field generating device internally
and configured to bear and convey two-component developer including
toner and magnetic carrier; a first regulating member configured to
regulate an amount of the developer born and conveyed by the
developer bearing member; a developer container section for
containing the developer scraped off by the first regulating
member; and a toner container section for supplying toner to the
developer bearing member, wherein the developer container section
has a second regulating member arranged upstream of the first
regulating member in a conveying direction of the developer on the
developer bearing member, the second regulating member is spaced
from the developer bearing member so as to regulate an increase of
a layer thickness of the developer on the developer bearing member
when the layer thickness of the developer is increased due to a
rise of a toner density of the developer, a surface of the second
regulating member facing the developer bearing member is spaced
from a surface of the developer bearing member such that a gap
between an end portion of the facing surface of the second
regulating member upstream in the developer conveying direction and
the surface of the developer bearing member is larger than a gap
between a downstream end portion of the facing surface of the
second regulating member and the surface of the developer bearing
member, the second regulating member having a base portion with a
first width and an end portion with a second width, the second
width being larger than the first width, the surface of the second
regulating member facing the developer bearing member being
provided on the end portion, a developer circulating portion is
formed for circulating developer obstructed by the second
regulating member, and a developer stagnated portion, where the
developer stands still when a toner density of the developer is
within a predetermined appropriate range, is formed in a toner
supplying path connecting the toner container section with the
developer circulating portion, such that a condition of taking the
toner into the developer is changed by a change of a contact
condition between the developer and the toner according to a change
of the toner density of the developer on the developer bearing
member, and the second regulating member is configured so as to
suppress a diffusion of the developer circulating portion.
31. An image forming apparatus according to claim 30, wherein, the
second regulating member includes a developer layer thickness
regulating section, which is spaced from the developer bearing
member so as to regulate an increase of a layer thickness of the
developer on the developer bearing member when the layer thickness
of the developer is increased due to a rise of a toner density of
the developer, and a circulating direction regulating section for
regulating a motion of the developer so that the developer
circulating section does not diffuse toward the toner container
section when the developer obstructed by the developer layer
thickness regulating section moves toward an upstream in the
developer conveying direction to form the developer circulating
portion.
32. An image forming apparatus according to claim 31, wherein the
circulating direction regulating section of the second regulating
member is a surface facing the developer bearing member extending
from the developer layer thickness regulating section toward the
upstream in the developer conveying direction.
33. An image forming apparatus according to claim 30, wherein the
surface facing the developer bearing member of the second
regulating member is non-magnetic.
34. An image forming apparatus according to claim 30, wherein the
surface of the second regulating member facing the developer
bearing member is elongated upstream in the developer conveying
direction.
35. An image forming apparatus according to claim 30, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
36. An image forming apparatus, comprising: an image bearing member
for bearing a latent image; and a developing apparatus for
developing the latent image, the developing apparatus including; a
developer bearing member having a magnetic field generating device
internally and configured to bear and convey two-component
developer including toner and magnetic carrier; a first regulating
member configured to regulate an amount of the developer born and
conveyed by the developer bearing member; a developer container
section for containing the developer scraped off by the first
regulating member; and a toner container section provided adjacent
to the developer container section for supplying toner to the
developer bearing member, wherein the developer container section
has a second regulating member arranged upstream of the first
regulating member in a conveying direction of the developer on the
developer bearing member, the second regulating member is spaced
from the developer bearing member so as to regulate an increase of
a layer thickness of the developer on the developer bearing member
when the layer thickness of the developer is increased due to a
rise of a toner density of the developer, a surface of the second
regulating member facing the developer bearing member is spaced
from a surface of the developer bearing member such that a gap
between an end portion of the facing surface of the second
regulating member upstream in the developer conveying direction and
the surface of the developer bearing member is larger than a gap
between a downstream end portion of the facing surface of the
second regulating member and the surface of the developer bearing
member, the second regulating member having a base portion with a
first width and an end portion with a second width, the second
width being larger than the first width, the surface of the second
regulating member facing the developer bearing member being
provided on the end portion, a developer circulating portion is
formed for circulating the developer obstructed by the second
regulating member, and a developer stagnated portion, where the
developer stands still when a toner density of the developer is
within a predetermined appropriate range, is formed in a toner
supplying path connecting the toner container section with the
developer circulating portion, such that a condition of taking the
toner into the developer is changed by a change of a contact
condition between the developer and the toner according to a change
of the toner density of the developer on the developer bearing
member, and a developing apparatus frame is configured so as not to
disturb an ear crack portion of the developer which is formed on
the developer bearing member by a magnetic pole opposite to the
developer circulating portion.
37. An image forming apparatus according to claim 36, wherein the
surface of the second regulating member facing the developer
bearing member is elongated upstream in the developer conveying
direction.
38. An image forming apparatus according to claim 36, wherein the
surface of the second regulating member facing the developer
bearing member is planar.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as
a copying machine, a facsimile, and a printer and to a developing
apparatus for a use in these apparatuses.
2. Discussion of the Background
Conventionally, as a developing apparatus for developing with
two-component developer including toner and carrier, there is known
a developing apparatus in which toner is taken into developer
according to behaviors of the developer without a need for a toner
density detecting device.
In such a developing apparatus, however, a toner feeding amount
depends upon whether or not a behavior of the developer is active
and whether or not the developer is abundant in respective places,
thereby partially causing the toner density to be unstable, which
easily results in fogging or an uneven image density.
Accordingly, in Japanese Patent Application No. 63-4282, for
example, to prevent fogging or an uneven density on an image as
described above, there is proposed a developing apparatus having
two toner supplying regulating members as described below. A first
toner supplying regulating member has a fixed end above a doctor
blade, which is a developer regulating member for regulating a
developer layer thickness on a developer bearing member. The first
toner supplying regulating member extends toward a toner supplying
tank which is a toner container section. A second toner supplying
regulating member is arranged closer to the toner supplying tank
than the first toner supplying regulating member. The second toner
supplying regulating member extends from the upper portion of the
developing apparatus downward, partitioning the developing
apparatus into a developer container and a toner supplying tank.
The lower free end of the second toner supplying regulating member
is on an extension line of a free end of the first toner supplying
regulating member or in the developer bearing member side.
In the above developing apparatus, a portion of the uppermost
developer layer on the developer bearing member, where developer is
relatively coarse and thereby toner is easily taken into, moves to
a regulating position of the above doctor blade in a condition of a
higher toner density than that of the developer layer on the
developing bearing member in the vicinity of the surface of the
developer bearing member. Such a movement of the portion of the
uppermost developer layer on the developing bearing member,
however, is prevented at the free end of the second toner supplying
regulating member before the developer layer enters into the
developer layer thickness regulating area enclosed by the first
toner supplying regulating member, the developer bearing member
surface, and the doctor blade. This prevents developer of an
extremely high toner density from being supplied to the developer
layer thickness regulating area, and only toner sufficiently
charged by a friction with magnetic particles is conveyed to the
developing area opposite to the image bearing member, such that a
fogged strip (background soiling) on an image and an uneven image
density in a direction perpendicular to a developer conveying
direction with the developer bearing member or the like are
prevented.
A developing apparatus previously proposed by the applicant of the
present invention and disclosed in Japanese Patent Laid-open
Publication No. 9-197833 is useful for dissolving the
above-described disadvantages while achieving down-sizing and a
lower cost of the apparatus.
The developing apparatus in Japanese Patent Laid-open Publication
No. 9-197833 internally has a magnetic field generating device, a
developer bearing member for bearing and conveying two-component
developer including toner and magnetic carrier, a first regulating
member for regulating an amount of developer born and conveyed by
the developer bearing member, a developer container section for
containing developer scraped off by the first regulating member,
and a toner container section arranged adjacent to the developer
container section for supplying toner to the developer bearing
member. The developing apparatus changes a toner take-in condition
of the developer on the developer bearing member by changing a
contact condition between the developer and the toner according to
a change of the toner density of the developer on the developer
bearing member. The developer container section has a second
regulating member arranged upstream of the first regulating member
in the conveying direction of the developer on the developer
bearing member, and the second regulating member is spaced from the
developer bearing member so as to regulate a passage of an increase
of the developer when the developer layer thickness is increased
due to a rise of the toner density of the developer on the
developer bearing member. According to this developing apparatus,
the toner and the magnetic carrier in the developer are agitated by
a cyclic motion of the developer in the developer container section
so as to prevent a charged amount of the toner from being reduced,
thereby avoiding an occurrence of an abnormal image such as an
image having an uneven image density or fogging while achieving
down-sizing and a lower cost of the apparatus by reducing the
number of components.
FIG. 1 illustrates an example of a developing apparatus related to
the above Japanese Patent Laid-open Publication No. 9-197833, and
FIG. 2 is an enlarged view of a main portion of the developing
apparatus for assistance in explaining behaviors of the developer
in the developing apparatus. The developing apparatus includes a
developing sleeve 1 as a developer bearing member containing a
permanent magnet as a magnetic field generating device, a first
regulating member 2 for regulating a layer thickness of developer
22, a developer containing case 4 as a developer containing member
for forming a developer container section 3 for containing
developer which is obstructed by the first regulating member 2
upstream of the first regulating member 2 in a rotary direction of
the developer bearing member, and a toner hopper 6 arranged
adjacent to the developer containing case 4 for containing toner.
The toner hopper 6 is in communication with the developer container
section 3 through a toner supplying path 7 as a toner supplying
aperture. Inside the toner hopper 6, there is provided an agitator
8 as a toner agitating member for conveying stored toner 5 to the
toner supplying path 7 while agitating the toner 5. Furthermore, at
the lower end of the developer containing case 4, there is provided
a second regulating member 9 spaced from the developing sleeve 1 so
as to regulate a passage of an increase of the developer 22 when a
layer thickness of the developer 22 is increased due to a rise of
the toner density of the developer 22 on the developing sleeve
1.
In the developing apparatus illustrated in FIGS. 1 and 2, when a
toner density of the developer 22 passing the first regulating
member 2 is within a predetermined appropriate range, the developer
22 scraped off by the second regulating member 9 forms a developer
stagnated portion 10. Then, the developer stagnated portion 10
clogs the toner supplying path 7, and taking-in of toner 5 from the
toner hopper 6 into the developer containing section 3 is stopped
in this condition. In the developer stagnated portion 10, the
developer 22 scraped off by the second regulating member 9 is
received by a toner supplying stage 14b, which is provided
integrally with a developing apparatus frame 14. The toner
supplying stage 14b is inclined downward to the developing sleeve 1
and has a predetermined length, thereby the developer 22 is
prevented from dropping to the toner hopper 6 by a motion of the
layer of the developer 22. Accordingly, a constant amount of the
developer 22 can always be maintained on the developer sleeve 1 and
a self-regulation for constantly supplying toner to the developer
22 is achieved. When a toner density of the developer in the
developer container section 3 is decreased by a toner consumption,
developer is taken into the developer container portion 3 from the
developer stagnated portion 10. Then, a volume of the developer
forming the developer stagnated portion 10 is decreased, by which
the toner 5 is started to be taken-in again into the developer 22
and is continued to be taken-in until the toner density of the
developer 22 reaches a predetermined density.
In the developing apparatuses proposed in Japanese Patent
Application No. 63-4282 and Japanese Patent Laid-open Publication
No. 9-197833, the layer thickness of the developer on the developer
bearing member in an axial direction of the developer bearing
member is regulated by a blade-like member as the second toner
supplying regulating member or the second toner regulating member
(hereinafter referred to as "second regulating member"), which is
arranged to face the developer bearing member. Because the above
second regulating member has just a small facing area to the
developer bearing member, if a gap between the second regulating
member and the developer bearing member is uneven in the axial
direction of the developer bearing member due to a processing
precision of the facing surface, it is very likely that a developer
layer is formed with an uneven thickness. Further, unevenness of
the developer layer thickness leads to an uneven amount of toner
taken into the developer, thereby sometimes causing an uneven image
density in the axial direction of the developer bearing member.
To solve the above-described problem, it is conceivable to increase
a processing precision of the facing surface of the second
regulating member, but it leads to an increase of cost of the
apparatus.
In the developing apparatus proposed in Japanese Patent Laid-open
Publication No. 9-197833, there is a disadvantage of causing an
uneven image density due to insufficiently charged toner which
locally exists. Referring to FIG. 2, the toner 5 is conveyed to the
developer container section 3 passing through a path as indicated
by an arrow in the drawing when the toner density of the developer
22 is lower than the appropriate range. The toner 5 is charged to
some extent by friction with the developer 22 when passing a
contact interface between the developer stagnated portion 10 and a
developer layer on the developing sleeve 1. At this time, the
charged amount for the toner 5 is almost proportional to a
magnitude of a frictional force between the developer stagnated
portion 10 and the developer layer on the developing sleeve 1.
Therefore, to achieve a sufficient charged amount for the toner 5,
this frictional force needs to be enough. The magnitude of the
frictional force is proportional to a conveying force of the
developer 22, in other words, to a magnitude of a normal component
of a magnetic force applied to the developer 22 by the magnetic
field generating device inside the developing sleeve 1.
The frictional force caused by the magnetic force is not enough to
charge all of the toner 5 taken into the developer 22 by a
sufficient amount, and therefore there locally remains
insufficiently charged toner 5. Accordingly, if the insufficiently
charged toner 5 flows into the developer container section 3 and is
conveyed to the developing area, an inferior image having, for
example an uneven density, is generated due to partially different
consumed toner amounts when printing an image requiring a large
amount of toner, such as a halftone image.
Further, in the above developing apparatus, toner is sometimes
directly put in contact with developer being conveyed by the
developer bearing member. If the toner is directly put in contact
with the developer and thereby the developer having a relatively
high toner density enters the developer container section, the
toner density of the developer cannot be sufficiently made uniform
only by a cyclic motion in the developer container section.
Accordingly, an uneven toner density may occur, thereby causing an
uneven image density.
Therefore, in Japanese Patent Application No. 10-50185, the
applicant of the present invention proposed to further include a
developer circulation forming device for forming a developer
circulating portion where developer which has been obstructed by
the second regulating member is circulated upstream of the second
regulating member in the developer conveying direction, and a
developer stagnated portion forming device for forming a developer
stagnated portion where developer stands still, when the developer
toner density is within a predetermined appropriate range, in a
toner supplying path connecting the above toner container section
with the developer circulating portion.
In this Japanese Patent Application, there is disclosed a
developing apparatus illustrated in FIG. 3 as an embodiment of the
invention. The developing apparatus illustrated in FIG. 3 is
characterized by having constructions described below in addition
to the construction of the prior application illustrated in FIG. 1.
That is, a toner supplying path 7 is configured to form a developer
stagnated portion 10 with a portion of a developer containing case
4 where the second regulating member 9 is formed and a partition 12
arranged so as to face the developer containing case 4, so that
developer in the toner supplying path 7 is stagnated in the
developer stagnated portion 10 when the toner density of the
developer is within an appropriate range. In downstream of the
developer stagnated portion 10 in the toner supplying path 7, there
is formed a developer circulating portion 11 having a size of
causing a cyclic motion of developer by the second regulating
member 9 and the developing apparatus frame 14, which is formed
integrally with the toner hopper 6 so as to enclose a lower portion
of the developing sleeve 1.
In the above developing apparatus, there is formed the
above-described developer circulating portion upstream of the
second regulating member in the developer conveying direction.
Further, the apparatus is configured such that, when the toner
density of the developer is within a predetermined appropriate
range, toner is prevented from being taken into developer at a
contact portion between the toner and the developer in the
developer stagnated portion where developer stands still. When the
toner density of the developer is decreased, the developer
stagnated portion disappears by being taken into the developer
circulating portion due to a decrease of a volume of the developer.
As a result, the developer is put in contact with toner in the
developer circulating portion and the toner is mixed with the
developer by agitation in the developer circulating portion before
the toner is taken into the developer on the developer bearing
member.
In this manner, when the toner density of the developer is
appropriate, a developer stagnated portion is formed, which then
prevents toner from being directly put in contact with the
developer conveyed by the developer bearing member. When the toner
density of the developer on the developer bearing member is
decreased after the toner has been consumed, developer having a
high density, in which toner has been previously mixed in the
developer circulating portion, is put in contact with the developer
carried on the developer bearing member and having a low density,
by which the toner is supplied to the developer and relatively even
toner replenishment is achieved.
In the developing apparatus illustrated in FIG. 3, however, a
developer bridge is sometimes formed between wall surfaces in the
toner supplying path 7, in other words, between the developer
containing case 4 and the partition 12, by the developer stagnated
in the developer stagnated portion 10 in the toner supplying path
7. By this bridge of the stagnant developer, supplying of toner
from the toner hopper 6 is stopped and a space is formed in a lower
portion of the developer stagnated portion 10, even when a volume
of developer is decreased in the lower portion of the developer
stagnated portion 10. Therefore, there is a possibility of causing
the toner density to be unstable.
Accordingly, in the above Japanese Patent Application, there is
also proposed a developing apparatus in which at least one wall
surface forming the developer stagnated portion in the toner
supplying path includes a moving member which is moved by an
operation of the developing apparatus. This developing apparatus is
capable of breaking the bridge of the stagnant developer stagnated
between the wall surfaces around the developer stagnated portion in
the toner supplying path by a motion of the moving member.
In the developing apparatus proposed in the above Japanese Patent
Application, however, sometimes the effect of breaking the bridge
of the stagnant developer is not enough. Therefore, it is desirable
to achieve a developing apparatus which allows a relatively even
toner replenishment without arranging the above partition 12.
It has been found, however, that if the partition 12 is removed
from a portion between the toner supplying path 7 and the toner
hopper 6 in the developing apparatus illustrated in FIG. 9, there
is a possibility that developer in the developer circulating
portion 11 overflows into the toner hopper 6 at agitation for
mixing the developer in the developer circulating portion 11 with
toner in the toner supplying path 7 put in contact with the
developer. This overflow occurs when the toner density of the
developer is decreased and the developer stagnated portion 10 is
taken into the developer circulating portion 11 and thereby the
developer circulating portion 11 extends toward the toner hopper 6
in the toner supplying path 7. That is, developer in a portion of
the developer circulating portion 11 distant from the developing
sleeve 1 diffuses due to a weak binding force of a magnetic force
applied by the developing sleeve 1 and thereby overflows into the
toner hopper 6 from the toner supplying path 7. If the developer
overflows into the toner hopper 6, a magnetic carrier amount of the
developer born by the developing sleeve 1 is reduced, by which the
toner density fluctuates.
In the developing apparatus illustrated in FIG. 3, when the toner
density of developer on the developing sleeve 1 is decreased, the
developer in the developer circulating portion 11 is put in contact
with the toner 5 in the toner supplying path 7 and the toner 5 is
mixed with the developer by agitation in the developer circulating
portion 11. The toner 5 thus agitated and mixed with the developer
is circulated by a cyclic motion of the developer circulating
portion 11 and taken into the developer on the developing sleeve 1
at the contact portion between the developer layer on the
developing sleeve 1 and the developer circulating portion 11. If
the developer on the developing sleeve 1 has an ear crack portion
(a gap between developer ears) at this point, the toner 5 is
actively taken into the ear crack portion of the developer. It is
assumed that this is because there are a lot of air gaps in the
developer having an ear crack portion in comparison with a portion
of the developer where the developer is close together and the
developer does not have any ear crack portions, and the toner 5 is
taken into the air gaps.
In the developing apparatus in FIG. 3, however, an ear crack
portion of the developer, which is formed in the toner supplying
path 7 by a magnetic pole opposite to the developer circulating
portion 11, collides with the developing frame 14, by which the ear
crack portion is disturbed. Therefore, the developer born by the
developing sleeve 1 by the magnetic pole and in contact with the
developer circulating portion 11 cannot form a stable ear crack
portion. Accordingly, there is a possibility that the toner cannot
be actively taken into the developer, and thereby the toner is not
sufficiently taken into the developer in some portions. This
unevenness in taking in toner causes an uneven toner density, by
which there is a possibility of causing an uneven image density in
forming a halftone image.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-discussed
and other problems and addresses the above-discussed and other
problems.
Preferred embodiments of the present invention provide a developing
apparatus and an image forming apparatus using the developing
apparatus, in which toner is taken into developer on a developer
bearing member according to a motion of the developer without a
need for a toner density detecting device and in which it is
possible to prevent an occurrence of an uneven image density by
keeping an even toner take-in amount in an axial direction of the
developer bearing member.
The preferred embodiments further provide a developing apparatus
and an image forming apparatus using the developing apparatus, in
which toner is taken into developer on a developer bearing member
according to a motion of the developer without a need for a toner
density detecting device and in which it is possible to prevent an
occurrence of an uneven image density caused by an insufficiently
charged toner.
The preferred embodiments further provide a developing apparatus
and an image forming apparatus using the same developing apparatus,
in which toner is taken into developer on a developer bearing
member according to a motion of the developer without a need for a
toner density detecting device and in which it is possible to
prevent a developer bridge from being formed by stagnant developer
and developer from overflowing into a toner container section so as
to stabilize a toner density and to achieve a more stable and even
image density.
The preferred embodiments further provide a developing apparatus
and an image forming apparatus using the same developing apparatus,
in which toner is taken into developer on a developer bearing
member according to a motion of the developer without a need for a
toner density detecting device and in which it is possible to form
a stable ear crack portion of developer so as to stabilize a toner
density and to achieve a more stable and even image density.
According to a preferred embodiment of the present invention, a
developing apparatus includes a developer bearing member having a
magnetic field generating device internally and configured to bear
and convey two-component developer including toner and magnetic
carrier, a first regulating member configured to regulate an amount
of the developer born and conveyed by the developer bearing member,
a developer container section for storing the developer scraped off
by the first regulating member, a second regulating member arranged
upstream of the first regulating member in a conveying direction of
the developer on the developer bearing member, and a toner
container section for supplying toner to the developer bearing
member. The developing apparatus changes a toner take-in condition
of the developer on the developer bearing member by changing a
contact condition between the developer and the toner according to
a change of a toner density of the developer on the developer
bearing member. A surface of the second regulating member facing
the developer bearing member has an area large enough to unify a
layer thickness of the developer on the image bearing member in the
axial direction of the developer bearing member.
Because of the surface of the second regulating member facing the
developer bearing member having an area large enough to unify the
layer thickness of the developer in the axial direction of the
developer bearing member, even if a gap between the second
regulating member and the developer bearing member is uneven in the
axial direction of the developer bearing member due to a processing
precision of the facing surface, the unevenness of the layer
thickness is eliminated by superimposition during a passage of the
developer through the facing surface of the second regulating
member and thereby an averaged layer thickness of the developer is
achieved. The averaged layer thickness of the developer makes it
possible to achieve an even toner take-in amount in the axial
direction of the developer bearing member, thereby preventing an
occurrence of an uneven image density.
According to another preferred embodiment of the present invention,
in the above developing apparatus, the developer container section
is formed downstream of the second regulating member in the
developer conveying direction, and the facing surface of the second
regulating member is extended toward an upstream in the developer
conveying direction on the developer bearing member.
In the immediately above developing device, because the developer
container section is formed upstream of the second regulating
member in the developer conveying direction, if the facing surface
of the second regulating member is extended toward a downstream of
the developer conveying direction, the capacity of the developer
container section is reduced, thereby reducing the capacity to
store the developer and as a result decreasing a developer life
disadvantageously. Accordingly, the facing surface of the second
regulating member is extended toward an upstream of the developer
conveying direction, and thereby it is possible to have a greater
volume of the developer container section and to elongate the
developer life correspondingly in comparison with a case in which
the second regulating member is extended downstream.
According to another preferred embodiment of the present invention,
in the above developing device, a deviation of a magnetic force of
the developer bearing member may be set within a range of giving no
effect on the layer thickness of the developer passing through the
second regulating member. Thereby, it is possible to prevent
unevenness in taking toner into the developer caused by a deviation
of the magnetic force of the developer bearing member in the axial
direction of the developer bearing member.
According to still another preferred embodiment of the present
invention, a developing apparatus includes a developer bearing
member having a magnetic field generating device internally and
configured to bear and convey two-component developer including
toner and magnetic carrier, a first regulating member configured to
regulate an amount of the developer born and conveyed by the
developer bearing member, a developer container section for
containing the developer scraped off by the first regulating
member, a second regulating member arranged upstream of the first
regulating member in a conveying direction of the developer on the
developer bearing member, and a toner container section for
supplying toner to the developer bearing member. The developing
apparatus changes a toner take-in condition of the developer on the
developer bearing member by changing a contact condition between
the developer and the toner according to a change of a toner
density of the developer on the developer bearing member. The
second regulating member is spaced from the developer bearing
member so as to regulate an increase of a layer thickness of the
developer on the developer bearing member when the layer thickness
thereof is increased due to a rise of the toner density of the
developer. A surface of the second regulating member facing the
developer bearing member is spaced from the surface of the
developer bearing member such that a gap between an end portion of
the facing surface of the second regulating member upstream in the
developer conveying direction and the surface of the developer
bearing member is larger than that between the downstream end
portion of the facing surface of the second regulating member and
the surface of the developer bearing member.
In the immediately above developing apparatus, the developer layer
including the toner born by the developer bearing member is
regulated by the second regulating member and the regulated
developer forms a developer stagnated portion. The developer of the
developer stagnated portion corresponding to the portion regulated
by the facing surface of the second regulating member receives a
reaction, which is a force acting in a direction against a
conveyance of the developer applied, from the facing surface of the
second regulating member. In addition, because the gap between the
upstream end portion in the developer conveying direction of the
facing surface of the second regulating member and the surface of
the developer bearing member is larger than that between its
downstream end portion and the surface of the developer bearing
member, a component force in the same direction as for the normal
component of a magnetic force generated by the magnetic field
generating device is generated in the reaction from the facing
surface. In other words, the developer in the developer stagnated
portion corresponding to the portion regulated by the facing
surface of the second regulating member receives the component
force of the reaction applied by the facing surface of the second
regulating member in addition to the magnetic force. This increases
a frictional force on a contact interface between the developer
stagnated portion and the developer layer born on the developer
bearing member. Therefore, the toner in the developer is
sufficiently charged, and thereby it is possible to prevent an
occurrence of an uneven image density caused by insufficiently
charged toner.
As a method of increasing a frictional force on the contact
interface between the developer stagnated portion and the developer
layer born on the developer bearing member, it is conceivable to
increase the normal component of the magnetic force generated by
the magnetic field generating device. However, increasing the
normal component of the magnetic force may cause a self-regulating
mechanism to not function appropriately for supplying toner in the
developing apparatus.
More specifically, the developer stagnated portion formed by the
developer regulated by the second regulating member becomes thicker
as an increase of the developer passed through the first regulating
member is regulated by the second regulating member. As the
developer stagnated portion becomes thicker, the upper portion of
the developer stagnated portion becomes further distant from the
developer bearing member, and thereby it becomes hard for the
developer to receive a conveying force of the developer bearing
member. The developer finally reaches a saturated layer thickness
where it is impossible to further increase the thickness. This
saturated layer thickness is approximately proportional to a
conveying force of the developer bearing member, in other words,
the normal component of the magnetic force received by the
developer. Therefore, the saturated layer thickness is increased as
the normal component becomes greater.
In the above developing apparatus, however, an amount of supplied
toner is automatically regulated at a constant level according to
an increase and a decrease of a volume of the developer stagnated
portion as described above, and therefore if the volume of the
developer stagnated portion, i.e., the saturated layer thickness of
the developer stagnated portion, is too large, a layer thickness of
the developer stagnated portion fluctuates in a wide range. Such a
wide range of the layer thickness fluctuation leads to an uneven
toner take-in amount in the axial direction of the developer
bearing member, thereby causing a toner density control to be
harder or deteriorating a property of the developer stagnated
portion to respond to supplying of toner. Thus, if the normal
component of the above magnetic force is increased, the
self-regulating mechanism for supplying toner may not function
appropriately, resulting in an occurrence of a poor image.
Therefore, according to another preferred embodiment of the present
invention, in the above developing apparatus, the normal component
of the magnetic force, which is applied to the developer by the
developer bearing member at the downstream end portion in the
developer conveying direction on the surface of the second
regulating member facing the developer bearing member, is set to be
stronger than the normal component of the magnetic force applied to
the developer by the developer bearing member at an upstream
portion of the facing surface of the second regulating member in
the developer conveying direction.
Accordingly, in the immediately above developing apparatus, because
a force of the developer bearing member bearing and conveying
developer is proportional to the normal component of the magnetic
force applied to developer by the developer bearing member, the
developer conveying force of the developer bearing member in the
upstream becomes smaller than that in the downstream in the
developer conveying direction, and thereby the saturated layer
thickness of the developer stagnated portion formed in the upstream
is decreased. Therefore, in the developer stagnated portion formed
in the upstream, the layer thickness fluctuation becomes more
sensitive to supplying of toner and the self-regulating mechanism
for supplying toner functions appropriately, while in the
downstream, the normal component of the magnetic force is set
stronger than that in the upstream so as to achieve a sufficient
frictional force on the contact interface between the developer
stagnated portion and the developer layer born by the developer
bearing member, thereby reliably preventing an insufficiently
charged toner.
In the immediately above developing device, regarding the surface
of the second regulating member facing the developer bearing
member, if a gap between the end-most portion of the facing surface
of the second regulating member upstream in the developer conveying
direction and the developer bearing member is smaller than the
layer thickness of the developer on the developer bearing member,
the developer on the developer bearing member is also regulated by
a substrate portion of the second regulating member. The developer
regulated by the substrate portion of the second regulating member
does not receive the component force of the reaction applied by the
facing surface of the second regulating member as described above,
and therefore the developer stagnated portion is easily diffused
and there is a possibility that the developer overflows into the
toner container section.
Accordingly, according to still another preferred embodiment of the
present invention, in the immediately above developing apparatus,
regarding the surface of the second regulating member facing the
developer bearing member, the gap between the end-most portion of
the surface of the second regulating member upstream in the
developer conveying direction and the developer bearing member is
set to be larger than the layer thickness of the developer on the
developer bearing member. Therefore, the developer layer on the
developer bearing member can be regulated only by the facing
surface of the second regulating member, and accordingly, diffusion
of the developer stagnated portion can be suppressed so as to
prevent the developer from overflowing into the toner container
portion.
According to still another preferred embodiment of the present
invention, a developing apparatus includes a developer bearing
member having a magnetic field generating device internally and
configured to bear and convey two-component developer including
toner and magnetic carrier, a first regulating member configured to
regulate an amount of the developer born and conveyed by the
developer bearing member, a developer container section for
containing the developer scraped off by the first regulating
member, and a toner container section for supplying toner to the
developer bearing member. The developer container section has a
second regulating member arranged upstream of the first regulating
member in a conveying direction of the developer on the developer
bearing member and the second regulating member is spaced from the
developer bearing member so as to regulate an increase of a layer
thickness of the developer on the developer bearing member when the
layer thickness of the developer is increased due to a rise of a
toner density of the developer. Further, a developer circulating
portion is formed for circulating the developer obstructed by the
second regulating member, and also, a developer stagnated portion,
where the developer stands still when a toner density of the
developer is within a predetermined appropriate range, is formed in
a toner supplying path connecting the toner container section with
the developer circulating portion, such that a contact condition
between the developer and the toner is changed according to a
change of the toner density of the developer on the developer
bearing member and thereby a condition of taking the toner into the
developer is changed. Furthermore, the second regulating member is
configured so as to suppress the diffusion of the developer
circulating portion.
In the immediately above developing apparatus, the developer
obstructed by the second regulating member moves upstream in the
developer conveying direction of the second regulating member to
form the developer circulating portion where the developer
circulates. When the toner density of the developer is within a
predetermined appropriate range, a developer stagnated portion
where the developer stands still is formed in the toner supplying
path connecting the developer circulating portion with the toner
container section so as to prevent the toner from being taken into
the developer at a contact portion between the toner and the
developer. When the toner density of the developer is decreased,
the developer in the developer stagnated portion is taken into the
developer circulating portion and thereby the developer stagnated
portion disappears, by which the developer is put in contact with
the toner in the toner supplying path and the developer is mixed
with the toner by agitation in the developer circulating portion.
In this condition, diffusion of the developer circulating portion
is suppressed by the second regulating member, and therefore the
developer circulating portion does not extend toward the toner
container section in the toner supplying path. Accordingly, the
developer in the developer circulating portion does not diffuse and
overflow into the toner container section. Thus, in the developing
apparatus of the present invention, it is possible to change the
contact condition between the developer and the toner according to
the toner density of the developer to change the toner take-in
condition of the developer without any partition between the toner
supplying path and the toner container section, and further
possible to prevent the developer in the developer circulating
portion from overflowing into the toner container section. Further,
unlike the case of arranging a partition, a bridge of developer
will not be formed by the stagnated developer on the wall surfaces
of the developer stagnated portion in the toner supplying path, and
therefore toner replenishment from the toner container section will
not be stopped by such a developer bridge. As a result, the toner
density can be stabilized.
According to another embodiment of the present invention, in the
immediately above developing apparatus, the second regulating
member includes a developer layer thickness regulating section,
which is spaced from the developer bearing member so as to regulate
an increase of a layer thickness of the developer on the developer
bearing member when the layer thickness of the developer is
increased due to a rise of a toner density of the developer, and a
circulating direction regulating section for regulating the motion
of the developer so that the developer circulating section does not
diffuse toward the toner container section when the developer
obstructed by the developer layer thickness regulating section
moves toward upstream in the developer conveying direction to form
the developer circulating portion. Thus, because the developer
circulating section regulates a moving direction of the developer
obstructed by the developer layer thickness regulating section of
the second regulating member toward upstream in the developer
conveying direction so that the developer circulating portion does
not diffuse to the toner container section, the developer
circulating portion does not extend toward the toner container
section and thereby the developer is prevented from overflowing
into the toner container section.
Further, according to another embodiment of the present invention,
in the immediately above developing apparatus, the circulating
direction regulating section of the second regulating member is a
surface facing the developer bearing member extending from the
developer layer thickness regulating section toward the upstream in
the developer conveying direction. When the developer obstructed by
the developer layer thickness regulating section of the second
regulating member moves toward the upstream of the developer layer
thickness regulating section in the developer conveying direction,
the developer moves along the surface of the second regulating
member facing the developer bearing member extending from the
developer layer thickness regulating section toward the upstream in
the developer conveying direction. The developer then diffuses to
the toner container section and is obstructed. In this manner, the
surface of the second regulating member facing the developer
bearing member extending from the developer layer thickness
regulating section toward the upstream in the developer conveying
direction regulates the developer moving direction toward upstream
in the developer conveying direction to such a direction that the
developer circulating portion does not diffuse to the toner
container section.
According to still another embodiment of the present invention, the
surface facing the developer bearing member of the second
regulating member may be non-magnetic. In the above developing
apparatus, if the facing surface of the second regulating member is
magnetic, a bridge of developer is formed between the surface of
the second regulating member facing the developer bearing member
and the developer bearing member. When the toner density is
decreased in the developer on the developer bearing member due to a
toner consumption, a force of obstructing taking toner into the
developer is increased by the bridge of the developer formed
between the facing surface of the second regulating member and the
developer bearing member, by which it may be caused that a required
amount of toner will not be taken into the developer. If the
above-described phenomenon is repeated, an abnormal image having,
for example, blank areas may occur. Therefore, a non-magnetic
material is used for the surface of the second regulating member
facing the developer bearing member, thereby preventing a developer
bridge from being formed between the facing surface of the second
regulating member and the developer bearing member. Thereby, even
when the toner density of the developer is decreased, a required
amount of toner can be taken into the developer.
According to still another preferred embodiment of the present
invention, a developing apparatus includes a developer bearing
member having a magnetic field generating device internally and
configured to bear and convey two-component developer including
toner and magnetic carrier, a first regulating member configured to
regulate an amount of the developer born and conveyed by the
developer bearing member, a developer container section for
containing the developer scraped off by the first regulating
member, and a toner container section provided adjacent to the
developer container section for supplying toner to the developer
bearing member. The developer container section has a second
regulating member arranged upstream of the first regulating member
in the conveying direction of the developer on the developer
bearing member, and the second regulating member is spaced from the
developer bearing member so as to regulate an increase of a layer
thickness of the developer when the layer thickness of the
developer is increased due to a rise of a toner density of the
developer. Further, a developer circulating portion is formed for
circulating the developer obstructed by the second regulating
member, and also, a developer stagnated portion, where the
developer stands still when a toner density of the developer is
within a predetermined appropriate range, is formed in a toner
supplying path connecting the toner container section with the
developer circulating portion, such that a contact condition
between the developer and the toner is changed according to a
change of the toner density of the developer on the developer
bearing member and thereby a condition of taking toner into the
developer is changed. Furthermore, a developing apparatus frame is
configured so as not to disturb an ear crack portion of the
developer, which is formed on the developer bearing member by a
magnetic pole opposite to the developer circulating portion.
Because the developing apparatus frame does not disturb an ear
crack portion of the developer which is formed on the developer
bearing member by a magnetic pole opposite to the developer
circulating portion, the ear crack portion of the developer can
stably be in contact with the developer circulating portion.
Further, due to such a stable ear crack portion, toner in the
developer circulating portion is actively taken into the developer
on the developer bearing member. Therefore, the toner density is
stabilized and an even image can be obtained even when a halftone
image is formed.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the present invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompany drawings, wherein:
FIG. 1 is a schematic drawing illustrating a developing apparatus
of prior art;
FIG. 2 is an enlarged view of a portion of the developing device of
FIG. 1 in the vicinity of a second regulating member of the
developing apparatus;
FIG. 3 is a schematic drawing illustrating a developing apparatus
according to an embodiment of a prior application of the
applicant;
FIG. 4 is a schematic drawing illustrating a configuration of a
developing apparatus according to an embodiment of the present
invention;
FIG. 5 is a schematic view for explaining a behaviour of a
developer in the developing apparatus;
FIG. 6 is another view for explaining a behaviour of the developer
in the developing apparatus;
FIG. 7 is another view for explaining a behaviour of the developer
in the developing apparatus;
FIG. 8 is a schematic drawing illustrating a configuration of a
developing apparatus according to another embodiment of the present
invention;
FIG. 9 is an enlarged view of a portion of the developing device of
FIG. 5 in the vicinity of a second regulating member of the
developing apparatus;
FIG. 10 is a schematic drawing illustrating a configuration of a
developing apparatus according to another embodiment of the present
invention; and
FIG. 11 is a schematic drawing for explaining the configuration of
the developing apparatus in FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views, preferred embodiments of the present invention are now
described, in which the present invention is applied to a
developing apparatus for use in an electrophotographic copying
machine as an image forming apparatus.
First Embodiment
FIG. 4 is a schematic drawing illustrating a configuration of a
developing apparatus according to an embodiment of the present
invention.
Referring to FIG. 4, the developing apparatus arranged on one side
of a photosensitive drum 13 as a latent image bearing member
includes a developing sleeve 1 as a developer bearing member, a
developer containing case 4, a first regulating member 2, a second
regulating member 9A, a toner hopper 6 as a toner container
section, a developing apparatus frame 14, and others.
The developing sleeve 1 is driven to rotate in a direction
indicated by an arrow in the diagram by a driving device which is
not shown. The developing sleeve 1 bears developer 22 including
toner and magnetic particles (carrier) on its surface. The
developing sleeve 1 is made of non-magnetic material, and has
inside a magnet (not shown) as a magnetic field generating device.
The magnet is arranged in a relative position unchangeable to the
developing apparatus 2.
The first regulating member 2 is arranged spaced from the
developing sleeve 1 so as to have a gap between its end portion and
an outer circumferential surface of the developing sleeve 1, and is
used to regulate a layer thickness of the developer 22. Upstream of
the first regulating member 2 in a rotary direction of the
developing sleeve 1, there is arranged the developer containing
case 4 as a developer containing member forming the developer
containing section 3 for containing developer which is obstructed
by the first regulating member 2. The developer containing case 4
is integrated with the developing apparatus frame 14. The developer
container section 3 is configured so as to have a space large
enough to cyclically move the developer 22 within the reach of the
magnetic force of the magnet in the developing sleeve 1.
The developer container section 3 is in communication with the
toner hopper 6 by a toner supplying path 7 as a toner supplying
aperture. The developing apparatus frame 14 has a raised portion
14a having an opposing surface 14b facing a bottom of the developer
containing case 4. A space between the bottom of the developer
containing case 4 and the opposing surface 14b forms the toner
supplying path 7. The developing apparatus frame 14 is integrated
with the toner hopper 6 so as to enclose a lower portion of the
developing sleeve 1.
In the toner hopper 6, there is arranged an agitator 8 as a toner
supplying device, which is rotated by a driving device (not shown)
for agitating toner 5 in the toner hopper 6 to deliver it toward
the toner supplying path 7. In addition, the toner hopper 6 has a
toner end detecting device 14C for detecting lack of the remainder
of toner 5 in the toner hopper 6.
Furthermore, at the lower end portion of the developer containing
case 4, a second regulating member 9A is formed so as to be in the
vicinity of the developing sleeve 1. The second regulating member
9A is spaced from the developing sleeve 1 so as to regulate an
increase of developer on the developing sleeve 1 when a layer
thickness of the developer is increased due to a rise of a toner
density of the developer on the developing sleeve 1. A shape of the
second regulating member 9A characterizing the present invention is
described in detail later.
In the above configuration, the toner 5 delivered from the inside
of the toner hopper 6 by the toner agitator 8 is supplied to the
developer 22 born by the developing sleeve 1 passing through the
toner supplying path 7 and then carried into the developer
container section 3. The developer 22 in the developer container
section 3 is born by the developing sleeve 1 and conveyed to a
position opposite to a circumferential surface of a photosensitive
drum 13, where only the toner 5 is electrostatically coupled to an
electrostatic latent image formed on the photosensitive drum 13, by
which a toner image is formed on the photosensitive drum 13.
Next, a behavior of the developer 22 at forming the above toner
image is described by referring to FIGS. 5, 6, and 7. If start
agent including magnetic carrier 22a only is set in the developing
apparatus, as illustrated in FIG. 5, the magnetic carrier 22a is
divided into one portion magnetically adhering to a surface of the
developing sleeve 1 and the other portion stored in the developer
container section 3. The magnetic carrier 22a stored in the
developer container section 3 cyclically moves at a moving rate of
1 mm/s or greater in a direction indicated by an arrow b by a
magnetic force of a magnet inside the developing sleeve 1 with a
rotation of the developing sleeve 1 in a direction indicated by an
arrow a (FIG. 6). Then, there is formed an interface X in a
boundary portion between a surface of the magnetic carrier 22a
magnetically adhering to the surface of the developing sleeve 1 and
a surface of the magnetic carrier 22a moving inside the developer
container section 3.
Next, when toner 5 is set in the toner hopper 6, the toner 5 is
supplied to the magnetic carrier 22a born by the developing sleeve
1 through the toner supplying path 7. Therefore, the developing
sleeve 1 bears developer 22 which is a mixture of the toner 5 and
the magnetic carrier 22a.
In the developer container section 3, because of a presence of the
stored developer 22, a force is applied to the developer 22
conveyed by the developing sleeve 1 in a direction of stopping the
conveyance of the developer 22. In this condition, when the toner 5
on the surface of the developer 22 born by the developing sleeve 1
is conveyed to the interface X, a frictional force among the
developer 22 in the vicinity of the interface X is reduced to
decrease the conveying force of the developer 22 in the vicinity of
the interface X, thereby decreasing a conveyance amount of the
developer 22 in the vicinity of the interface X.
On the other hand, the developer 22 upstream of a junction Y in a
rotary direction of the developing sleeve 1 is not affected by the
force to stop the conveyance thereof like the one applied to the
developer 22 conveyed by the developing sleeve 1 in the developer
container section 3 described above. Therefore, due to lost balance
of a conveyance amount between the developer 22 conveyed to the
junction Y and the developer 22 conveyed on the interface X, a
multiple collision of the developer 22 is caused, by which the
position of the junction Y rises as illustrated in FIG. 6 to
increase the layer thickness of the developer 22 including the
interface X. In addition, the layer thickness of the developer 22
which has passed the first regulating member 2 increases gradually
and the increased developer 22 is scraped off by the second
regulating member 9A in a regulating position of the second
regulating member 9A.
When the developer 22 which has passed the first regulating member
2 has reached a predetermined toner density, as illustrated in FIG.
7, a laminar increase of the developer 22 which has been scraped
off by the second regulating member 9A clogs the toner supplying
path 7 and thereby take-in of the toner 5 is completed in this
condition. At this point, the volume of the developer 22 is
increased due to a rise of the toner density in the developer
container section 3, thereby narrowing the space inside the
developer container section 3. As a result, a moving rate at which
the developer 22 cyclically moves in a direction indicated by the
arrow b in this diagram is lowered.
In the layer of the developer 22 formed so as to clog the toner
supplying path 7, the developer 22 scraped off by the second
regulating member 9A is received by the opposing surface 14b after
moving as indicated by an arrow c in FIG. 7 at a moving rate of 1
mm/s or greater. Because the opposing surface 14b is inclined
downward at an angle to the developing sleeve 1 and has a
predetermined length, it is possible to prevent the developer 22
from being dropped to the toner hopper 6 by a motion of the layer
of the developer 22, such that the constant amount of the developer
22 is always kept and thereby a self-regulation of a constant toner
replenishment is achieved at all times.
Next, a description is made for a shape of the second regulating
member 9A, which is a characterizing portion of this
embodiment.
The surface 16A of the second regulating member 9A facing the
developing sleeve 1 is configured to have an area large enough to
unify a layer thickness of the developer 22 in an axial direction
of the developing sleeve 1. Specifically, the surface 16A of the
second regulating member 9A facing the developing sleeve 1 has a
surface shape along a circumferential surface of the developing
sleeve 1 and extends toward the upstream in the conveying direction
of the developer 22 on the developing sleeve 1. In this manner, the
facing surface 16A of the second regulating member 9A of this
embodiment is configured to have an area larger than the facing
surface of the second regulating member having a blade shape
according to the prior application as described above.
In the above configuration, when the developer 22 including the
toner 5 reaches the second regulating member 9A, the layer
thickness of the developer 22 is regulated by the facing surface
16A of the second regulating member 9A. At this time, even if there
is an uneven gap between the second regulating member 9A and the
developing sleeve 1 in the axial direction of the developing sleeve
1 due to a processing precision of the facing surface 16A, the
unevenness of the layer thickness of the developer 22 is eliminated
by superimposition while the developer 22 passes the facing surface
16A having a large opposing area and thereby the layer thickness of
the developer 22 is averaged in the axial direction of the
developing sleeve 1. As the layer thickness of the developer 22 is
averaged, the amount of toner 5 taken into the developer 22 is made
constant.
As described above, by configuring the facing surface 16A of the
second regulating member 9A facing the developing sleeve 1 so as to
have an area large enough to unify the layer thickness of the
developer 22 in the axial direction of the developing sleeve 1, the
amount of toner 5 taken into the developer can be made constant,
and thereby an occurrence of an uneven image density is
prevented.
In addition, in the developing apparatus illustrated in FIG. 4, the
facing surface 16A of the second regulating member 9A is arranged
so as to extend toward the upstream in the developer 22 conveying
direction. Because the developer container section 3 is formed
downstream of the second regulating member 9A in the developer
conveying direction, if the facing surface 16A should extend toward
the downstream, a capacity of the developer container section 3 is
reduced to decrease the developer 22 to be stored, which leads to a
reduction of a developer life disadvantageously. In this developing
apparatus, however, the facing surface 16A extends toward the
upstream in the developer conveying direction, by which the
capacity of the developer container section 3 can be enlarged in
comparison with a case of the facing surface 16A extending toward
the downward, thereby elongating the developer life
correspondingly.
It should be noted that, however, a magnetic force distribution is
preferably uniform in the axial direction of the developing sleeve
1 so as not to make an uneven layer thickness of the developer 22
passing the facing surface 16A of the second regulating member
9A.
Therefore, in the developing apparatus in FIG. 4, a deviation of
the magnetic force of the developing sleeve 1 is set to a value
within a range of keeping constant a layer thickness of the
developer 22 passing the second regulating member 9A. Specifically,
by considering a torsion in the axial direction of the sleeve 1
which may occur in a magnetic technique or in a magnetically
adhering process or the like, the deviation of the magnetic force
of the developing sleeve 1 in the facing surface 16A is set so as
to be within a range of 25%. Accordingly, unevenness of the layer
thickness of the developer 22 can be reduced, thereby preventing
toner 5 from being taken into the developer 22 inconstantly in the
axial direction of the developing sleeve 1.
[Second Embodiment]
Referring to FIG. 8, there is illustrated a configuration of a
developing apparatus according to another embodiment of the present
invention.
The basic constitution and operation of the developing apparatus in
FIG. 8 are the same as those for the developing apparatus according
to the first embodiment, and therefore identical reference
characters are used to designate members substantially identical or
corresponding to those of the first embodiment, with omitting a
description of the identical members and describing only a
characterizing portion of this embodiment.
Referring to FIG. 9, there is illustrated an enlarged view of a
portion in the vicinity of a second regulating member 9B in the
developing apparatus in FIG. 8. In this embodiment, the second
regulating member 9B is configured to have a shape effective to
have a large frictional force described above so that the toner 5
can be sufficiently charged. Specifically, as illustrated in FIG.
9, regarding a facing surface 16B of the second regulating member
9B facing the developing sleeve 1, a gap Ga between an upstream end
portion in a developer conveying direction and a surface of the
developing sleeve 1 is wider than a gap Gb between a downstream end
portion and a surface of the developing sleeve 1.
In the above configuration, the layer of the developer 22 including
toner 5 born by the developing sleeve 1 is regulated by the second
regulating member 9B, and a developer stagnated portion 10 is
formed by the regulated developer 22. At this time, the developer
22 in a portion of the developer stagnated portion 10, which is
regulated by the facing surface 16B, receives a reaction, which is
a force acting in a direction of interfering with the conveyance of
the developer 22, from the facing surface 16B of the second
regulating member 9B. In addition, the facing surface 16B is
tapered so that the gap Ga is larger than the Gb, and therefore a
component force is generated in the reaction of the facing surface
16B applied to the developer stagnated portion 10, in the same
direction as for a normal component of a magnetic force generated
by the magnet in the developing sleeve 1. In other words, the
developer 22 in the portion of the developer stagnated portion 10,
which is regulated by the facing surface 16B, receives the
component force of the reaction from the facing surface 16B in
addition to the magnetic force. This increases a frictional force
on a contact interface between the developer stagnated portion 10
and the layer of the developer 22 born by the developing sleeve 1.
Therefore, the toner 5 in the developer 22 is sufficiently charged,
and thereby an occurrence of an uneven image density caused by
insufficiently charged toner is prevented.
As a method of increasing the frictional force on the contact
interface between the developer stagnated portion 10 and the layer
of the developer 22 born by the developing sleeve 1, it is
conceivable to increase a normal component of a magnetic force
generated by a magnet roller inside the developing sleeve 1.
If the normal component of the magnetic force is increased,
however, there is a possibility that the self-regulation mechanism
of the developing apparatus for supplying toner to developer will
not function appropriately. Specifically, the developer stagnated
portion 10 formed by the developer 22 regulated by the second
regulating member 9B is increased in thickness whenever the
increase of the developer 22 passing the first regulating member 2
is regulated by the second regulating member 9B. As the developer
stagnated portion 10 is increased in thickness, the upper portion
is distant further from the developing sleeve 1 and therefore it
becomes harder to receive a conveying force from the developing
sleeve 1, and then the developer stagnated portion 10 reaches a
saturated layer thickness at which the thickness cannot be
increased any more. This saturated layer thickness becomes
necessarily larger as the conveying force of the developing sleeve
1 is increased. Because the conveying force of the developing
sleeve 1 is almost proportional to the normal component of the
magnetic force applied to the developer 22, as the normal component
is increased, the saturated layer thickness becomes larger.
A too large volume of the developer stagnated portion 10, i.e., a
too large saturated layer thickness of the developer stagnated
portion 10, enlarges a range of a fluctuation of the layer
thickness of the developer stagnated portion 10. If the range of
the fluctuation of the layer thickness is excessively large, there
is a possibility that toner 5 will be taken into the developer at
an uneven rate in the axial direction of the developing sleeve 1,
thereby leading to a difficulty of the toner density control or to
a deterioration of a property of the developer stagnated portion 10
to respond to supplying of toner. In this manner, an increased
normal component of the magnetic force may cause a malfunction of
the self-regulation mechanism for supplying toner, which results in
an occurrence of a defective image.
Therefore, in this embodiment, the normal component of the magnetic
force, which is applied to the developer 22 by the magnet in the
developing sleeve 1 at the downstream end portion of the facing
surface 16B of the second regulating member 9B in the developer
conveying direction, is set so as to be greater than the normal
component of the magnetic force applied to the developer 22 by the
magnet in the upstream in the developer conveying direction.
Because a force of the developing sleeve 1 for bearing and
conveying the developer 22 is proportional to the normal component
of the magnetic force applied to the developer 22, the developer
conveying force of the developing sleeve 1 in the upstream becomes
smaller than that in the downstream. Therefore, the saturated layer
thickness of the developer stagnated portion 10 formed in the
upstream is smaller than that in the downstream. Accordingly, in
the developer stagnated portion 10 formed in the upstream, the
layer thickness is more sensitively fluctuated in response to
supplying of toner, by which the self-regulation mechanism for
supplying toner functions appropriately. On the other hand, the
normal component of the magnetic force in the downstream is set
greater than that in the upstream so as to achieve a sufficiently
large frictional force on the contact interface between the
developer stagnated portion 10 and the layer of the developer 22
born by the developing sleeve 1, by which a lack of charging can be
prevented more reliably.
To set the normal component of the magnetic force of the magnet in
the developing sleeve 1 as described above, it is possible to use a
method of, for example, designing the apparatus so as to have a
peak of the magnetic pole of the developing sleeve 1 in the
vicinity of the downstream end portion of the facing surface 16B in
the developer conveying direction.
In addition, it is preferable to set the gap Ga at the end-most
portion of the facing surface 16B in the upstream in the developer
conveying direction so as to be larger than the layer thickness of
the developer 22 on the developing sleeve 1. This is because the
gap Ga smaller than the layer thickness of the developer 22 on the
developing sleeve 1 forces the developer 22 to be regulated by a
substrate portion of the second regulating member 9B as well as by
the facing surface 16B of the second regulating member 9B and
thereby the developer stagnated portion 10 is easily diffused,
because a component force of the reaction from the facing surface
16B is not applied to the developer regulated by the substrate
portion as described above, thus causing a possibility that the
diffused developer will overflow into the toner hopper 6,
Therefore, in this embodiment, the gap Ga is arranged so as to be
larger than the layer thickness of the developer on the developing
sleeve 1 as illustrated in FIG. 9. Specifically, the magnet is
arranged inside the sleeve 1 so as not to expose the peak of the
magnetic pole in the normal direction to the toner supplying path
7, and under this condition, a gap Gc between the developing sleeve
1 and the developing apparatus frame 14 and the gap Ga are arranged
so as to satisfy a relationship represented by an inequality:
Gc<Ga. In this configuration, the layer thickness of the
developer 22 born by the developing sleeve 1 is not larger than the
gap Gc even at its maximum. Therefore, in a condition that the
relationship represented by the inequality: Gc<Ga is satisfied,
the gap Ga is larger than the layer thickness of the developer 22,
and therefore the developer 22 on the developing sleeve 1 can be
regulated only by the facing surface 16B. Accordingly, the
diffusion of the developer stagnated portion 10 can be suppressed
to prevent the developer 22 from overflowing into the toner hopper
6.
[Third Embodiment]
Referring to FIG. 10, there is illustrated a configuration of a
developing apparatus according to another embodiment of the present
invention.
In the developing apparatus of this embodiment, a toner supplying
path 7 is configured so as to form, with the portion of a developer
containing case 4 where a second regulating member 9C is formed and
the portion of a developing apparatus frame 14 facing the developer
containing case 4, a developer stagnated portion 10 where developer
is stagnated in the toner supplying path 7 when a toner density of
developer (i.e., a percentage by weight of toner in developer) is
within an appropriate range. In downstream of the developer
stagnated portion 10 in the toner supplying path 7, there is formed
a developer circulating portion 11 for causing a cyclic motion in
the developer with the second regulating member 9C and the
developing apparatus frame 14. In the developing apparatus
illustrated in FIG. 10, identical reference characters are used to
designate substantially identical or corresponding members to the
first embodiment and their description is omitted here.
Because stagnant developer standing in the developer stagnated
portion 10 is put in a still condition, at a contact portion
between toner 5 in a toner hopper 6 and the stagnant developer, the
stagnant developer is never mixed with the toner 5 and therefore
the toner 5 is not taken into the stagnant developer there.
In the developer circulating portion 11, at a consumption of toner
in the developer in the developer circulating portion 11, the
volume of developer is decreased, and thereby the stagnant
developer of the developer stagnated portion 10 is taken into the
developer circulating portion 11 to be disappeared. Then, when the
toner 5 delivered from the toner hopper 6 is put into contact with
the developer circulating portion 11, the toner 5 is taken into
circulating developer in the developer circulating portion 11, by
which a toner density of the developer is increased. When the
volume of the developer is increased as a result of taking the
toner 5 into the developer, excess developer forms a developer
stagnated portion 10 again to prevent the toner 5 from being taken
in from the toner hopper 6.
Then, in the developer circulating portion 11, the developer having
a high toner density after having been mixed with the toner 5 is
put into contact with developer having a low toner density as a
result of the toner conveyed by the developing sleeve 1 having been
consumed, by which the toner 5 is supplied to the developer from
the contact portion and thereby substantially even toner
replenishment is achieved.
Next, a description is made for a shape of the second regulating
member 9C which is a characterizing portion of this embodiment. In
FIG. 10, the facing surface 16C of the second regulating member 9C
facing the developing sleeve 1 has a developer layer thickness
regulating section 15 spaced from the developing sleeve 1 so as to
regulate an increase of developer when a layer thickness of the
developer is increased due to a rise of a toner density of the
developer on the developing sleeve 1. In addition, the facing
surface 16C extends toward the upstream of the developer layer
thickness regulating section 15 in the developer conveying
direction and is tapered so that a gap to the developing sleeve 1
is gradually narrowed from the upstream toward the downstream in
the developer conveying direction.
The developer obstructed by the second regulating member 9C moves
toward the upstream of the developer layer thickness regulating
section 15 in the developer conveying direction and forms the
developer circulating portion 11. At this time, the developer moves
along the facing surface 16C extending toward the upstream of the
developer layer thickness regulating section 15 in the developer
conveying direction. In this manner, the facing surface 16C
extending upstream in the developer conveying direction functions
as a circulating direction regulating section for regulating the
developer moving direction toward the upstream in the developer
conveying direction so that the developer circulating portion 11
does not diffuse to the toner hopper 6. Thus, the developer
circulating portion 11 is stopped to diffuse to the toner hopper 6,
by which the developer circulating portion 11 having a thin and
stable shape is formed toward the upstream in the developer
conveying direction.
As described above, when the toner density of the developer is
decreased in the above condition, stagnant developer in the
developer stagnated portion 10 is taken into the developer
circulating portion 11 and thereby the developer stagnated portion
10 is eliminated, by which the developer in the developer
circulating portion 11 is put into contact with toner in the toner
supplying path 7 and the developer is mixed with the toner by
agitation in the developer circulating portion 11. At this point,
the developer in the portion distant from the developing sleeve 1
has a weak binding force of the magnetic force applied by the
magnet inside the developing sleeve 1 and therefore there is a
possibility that the developer diffuses and overflows from the
toner supplying path 7 to the toner hopper 6. In the developing
apparatus of this embodiment, however, the facing surface 16C of
the second regulating member 9C regulates the developer moving
direction toward the upstream in the developer conveying direction
so that the developer circulating portion 11 does not diffuse to
the toner hopper 6. Therefore, the developer circulating portion 11
does not extend toward the toner hopper 6, and thereby the
developer is prevented from overflowing into the toner hopper
6.
In this manner, without a partition between the toner supplying
path 7 and the toner hopper 6, it is possible to prevent developer
from overflowing into the toner hopper 6. Further, there is no
possibility that stagnant developer will form a developer bridge on
wall surfaces of the developer stagnated portion 10 in the toner
supplying path 7. As a result, it is possible to stabilize the
toner density and to achieve a more stable and even image
density.
The shape of the second regulating member 9C for preventing the
diffusion of the developer circulating portion 11 is not limited to
the one having the tapered facing surface 16C with the gap to the
developing sleeve 1 gradually narrowing from the upstream to the
downstream in the developer conveying direction, but any shape can
be applied only if it has a developer layer thickness regulating
section spaced from the developing sleeve 1 so as to regulate an
increase of developer when a layer thickness of the developer is
increased due to a rise of a toner density of the developer on the
developing sleeve 1 and a circulating direction regulating section
for regulating the developer moving direction so that the developer
circulating portion 11 does not diffuse to the toner hopper 6 when
the developer obstructed by the developer layer thickness
regulating section moves upstream in the developer conveying
direction and forms the developer circulating portion 11.
In the developing apparatus illustrated in FIG. 10, if the facing
surface 16C of the second regulating member 9C is made of magnetic
material, a bridge of developer is formed between the facing
surface 16C and the developing sleeve 1. When the toner density of
the developer on the developing sleeve 1 is decreased by a
consumption of toner, a force of obstructing taking toner into the
developer is increased by a developer bridge formed between the
facing surface 16C and the developing sleeve 1, which causes a
possibility that a required amount of toner will not be taken into
the developer. If the above-described phenomenon is repeated, an
abnormal image having, for example a blank area, may be
generated.
Therefore, in this embodiment, the facing surface 16C of the second
regulating member 9C is made of non-magnetic material. This
prevents a developer bridge from being formed between the facing
surface 16C and the developing sleeve 1. Accordingly, when the
toner density of the developer is decreased, a required amount of
toner can be taken into the developer.
Next, conditions of achieving the above behaviors of the developer
and the toner 5 are described below by giving an example.
As illustrated in FIG. 11, regarding magnetic poles of the magnetic
field generating device arranged inside the developing sleeve 1,
pole P1 is assumed to be the magnetic pole facing the
photosensitive drum 13, pole P2 and pole P3 are arranged
counterclockwise with the pole P1 as a reference, and pole P4 is
arranged in a position opposite to the developer container section
3.
In this condition, in order to form a developer stagnated portion
10 in the contact portion between the toner 5 and the developer
when the developer in the developer circulating portion 11 reaches
a predetermined density by taking toner into the developer and to
suppress a diffusion of the developer circulating portion 11 when
the developer circulating portion 11 takes in the developer
stagnated portion 10 when the developer toner density is decreased
as described above, it is necessary to appropriately set the
arrangement and magnetic force of the poles P3 and P4, the shape
and position of the second regulating member 9C, the shape and
position of the space for circulating developer formed in front of
the second regulating member 9C, and the relative positional
relationship of the toner supplying path 7.
The following describes an example of appropriate conditions of the
relative positional relationship of the above portions of the
developing apparatus having the configuration illustrated in FIG.
11, which was obtained on the basis of experimental results. Angle
formed by pole P3 and a vertical: .theta.1=127 deg. Maximum
magnetic flux density in a normal direction on a circumferential
surface of the developing sleeve 1 of pole P3: 53 mT Angle formed
by pole P4 and a vertical: .theta.2=35 deg. Maximum magnetic flux
density in a normal direction on a circumferential surface of the
developing sleeve 1 of pole P4: 56 mT Angle formed by the second
regulating member 9 and a horizontal: .theta.3=14 deg. Angle formed
by a facing surface of the second regulating member 9 facing the
developing sleeve 1 and a vertical: .theta.4=24 deg. Gap between
the second regulating member 9 and a surface of the developing
sleeve 1: a=0.6 mm Width of an aperture in the toner supplying path
7: b=5.4 mm Diameter of the developing sleeve 1: c=.phi.16 mm
For the above condition settings, the following developer is used:
Carrier: Magnetite or iron; 40 to 50 .mu.m Toner: Amount of
magnetic material; 15 to 40 wt % Amount of silica; 0.5 to 1.0 wt %
Coating ratio of toner to carrier; 50 to 120 wt % Q/M; 10 to 30
.mu.c/g
With the above condition settings, the behaviors of developer and
toner as described above can be achieved, thereby stabilizing the
toner density of the developer.
The above conditions are described just as an example for the
developing apparatus according to this embodiment, and the above
behaviors of developer and toner can be achieved with other
combinations of these conditions.
Next, a description is made below for an arrangement of the
magnetic poles opposite to the developer circulating portion 11 and
the developing apparatus frame 14.
In the above developing apparatus, when the toner density of the
developer is decreased, toner is mixed with developer by agitation
in the developer circulating portion 11 and then the toner is taken
into a developer layer on the developing sleeve 1 from the contact
portion between the developer layer on the developing sleeve 1 and
the developer circulating portion 11. At this time, if the
developer on the developing sleeve 1 has an ear crack portion, the
toner is actively taken into the developer in the ear crack
portion. It is assumed that this is because there are a lot of air
gaps in the developer which can take in the toner in the ear crack
portion in comparison with a portion of the developer where the
developer is close together.
In the developing apparatus illustrated in FIG. 10, the pole P3
which is a magnetic pole opposite to the developer circulating
portion 11 is completely exposed to the toner supplying path 7, by
which the developing apparatus frame 14 does not disturb the ear
crack portion of the developer on the developing sleeve 1 which
appears in a position corresponding to the peak of the pole P3.
Therefore, a stable ear crack portion is formed so as to be in
contact with the developer circulating portion 11 on the developing
sleeve 1. With this stable ear crack portion, toner in the
developer circulating portion 11 can be actively taken into the
developer on the developing sleeve 1. Therefore, the toner density
is stabilized and an even image is obtained even in forming a
halftone image.
As an example for comparison, in a developing apparatus illustrated
in FIG. 3, a peak of a magnetic pole opposite to the developer
circulating portion 11 of the magnetic field generating device
inside the developing sleeve 1 is obstructed by the opposing
developing apparatus frame 14 and therefore it is not exposed to
the toner supplying path 7. Accordingly, the ear crack portion of
developer on the developing sleeve 1, which appears in a position
corresponding to the peak of the pole P3, collides with the
developing apparatus frame 14 to be disturbed. Therefore, the
developer in contact with a circulating space of the developer
circulating portion 11 on the developing sleeve 1 does not form a
stable ear crack portion and cannot actively take toner in the
developer circulating portion 11 from the ear crack portion.
Accordingly, the toner density becomes unstable, thereby causing a
possibility of generating an uneven image density in forming a
halftone image.
Numerous additional modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the present invention may be practiced otherwise than
specifically described herein.
This document claims priority and contains subject matter related
to Japanese patent applications No. 11-126007, No. 11-125601, No.
11-203408 and No. 12-xxxxx filed in the Japanese Patent Office on
May 6, 1999, May 6, 1999, Jul. 16, 1999 and Mar. xx, 2000,
respectively, and the entire contents of which are hereby
incorporated herein by reference.
* * * * *